Process and apparatus for producing metallic glass

ABSTRACT

A process and an apparatus for producing metallic glass which are capable of producing a bulk amorphous alloy of desired shape, in particular, a bulk amorphous alloy of desired final shape are provided. In the present invention, the molten metal at a temperature above the melting point is selectively cooled at a rate higher than the critical cooling rate, and the product comprises single amorphous phase which is free from the crystalline phase formed by the development of crystal nuclei through nonuniform nucleation. The present invention is capable of producing the bulk amorphous alloy which is free from casting defects such as cold shuts and which has excellent strength properties in a simple process at a high reproducibility. Accordingly, a bulk metallic glass of desired shape is produced by filling a metal material in a hearth; melting the metal material by using a high-energy heat source which is capable of melting the metal material; pressing the molten metal at a temperature above the melting point of the metal material to deform the molten metal into the desired shape by at least one of compressive stress and shear stress at a temperature above the melting point, while avoiding the surfaces of the molten metal cooled to a temperature below the melting point of the metal material from meeting with each other during the pressing; and cooling the molten metal at a cooling rate higher than the critical cooling rate of the metal material simultaneously with or after the deformation to produce the bulk metallic glass of desired form.

TECHNICAL FIELD

[0001] This invention relates to processes and apparatus for producingbulk metallic glasses (bulk amorphous metals) of various desired shapesexhibiting excellent strength properties which are free from the socalled cold shuts, which are the amorphous regions formed by meeting ofthe surfaces of the molten metal.

BACKGROUND ART

[0002] Various methods for producing amorphous materials have beenproposed. Exemplary such methods include the method wherein a moltenmetal or alloy in liquid state is solidified by quenching and theresulting quenched metal (alloy) powder is compacted at a temperaturebelow the crystallization temperature to produce a solid of thepredetermined configuration having the true density; and the methodwherein a molten metal or alloy is solidified by quenching to directlyproduce an ingot of the amorphous material having the predeterminedconfiguration. Almost all amorphous material produced by suchconventional methods had an insufficiently small mass, and it has beenimpossible to produce a bulk material by such conventional methods.Another attempt for producing a bulk material is solidification of thequenched powder. Such attempt, however, has so far failed to produce asatisfactory bulk material.

[0003] For example, the amorphous material produced in small mass havebeen produced by melt spinning, single roll method, planar flow castingand the like whereby the amorphous material in the form of thin strip(ribbon) in the size of, for example, about 200 mm in the strip widthand about 30 μm in the strip thickness are produced. Use of suchamorphous materials for such purposes as the core material of atransformer has been attempted, but so far, most amorphous materialsproduced by such methods are not yet put to industrial use. Thetechniques that have been used for solidification forming or compactionmolding the quenched powder into an amorphous material of a small massinclude CIP, HIP, hot press, hot extrusion, electro-discharge plasmasintering, and the like. Such techniques, however, suffered from theproblems of poor flow properties due to the minute configuration, andthe problem of temperature-dependent properties, namely, incapability ofincreasing the temperature above the glass transition temperature. Inaddition, forming process involves many steps, and the solidificationformed materials produced suffer from insufficient properties as a bulkmaterial. Therefore, such methods are still insufficient.

[0004] Recently, the inventors of the present invention found that anumber of ternary amorphous alloys such as Ln—Al—TM, Mg—Ln—TM, Zr—Al—TM,Hf—Al—TM and Ti—Zr—TM (wherein Ln is a lanthanide metal, and TM is atransition metal of the Groups VI to VIII) ternary systems have lowcritical cooling rates for glass formation of the order of 10² K/s, andcan be produced in a bulk shape with thickness up to about 9 mm by usinga mold casting or a high-pressure die casting method.

[0005] It has been, however, impossible to produce a large-sizedamorphous alloy material of desired configuration irrespective of theproduction process. There is a strong needs for the development of a newsolidification technique capable of producing a large-sized amorphousalloy material and an amorphous alloy having a still lower criticalcooling rate for enabling the production of the amorphous metal materialof larger size.

[0006] In view of such situation, the inventors of the present inventionproceeded with the investigation of the bulk amorphous alloy using theternary alloy by focusing on the effect of increasing the number of thealloy constituents each having different specific atom size asexemplified by the high glass formation ability of the ternary alloyprimarily attributable to the optimal specific size distribution of theconstituent atoms that are mutually different in size by more than 10%.As a consequence, the inventors found amorphous alloys of Zr—Al—Co—Ni—Cualloy systems, Zr—Ti—Al—Ni—Cu alloy systems, Zr—Ti—Nb—Al—Ni—Cu alloysystems, and Zr—Ti—Hf—Al—Co—Ni—Cu alloy systems that have significantlylower critical cooling rates in the range of from 1 to 100 K/s, anddisclosed in U.S. Pat. No. 5,740,854 (Unites States Patent correspondingto JP-A 6-249254) that alloys of Zr—Al—Ni—Cu alloy systems may beproduced into a bulk amorphous alloy material with a size of up to 16 mmin diameter and 150 mm in length by quenching the melt in a quartz tubein water.

[0007] The inventors of the present invention also disclosed in U.S.Pat. No. 5,740,854 and JP-A 6-249254 that the resulting bulk amorphousalloy material has a tensile strength of as high as 1500 MPa comparableto the compressive strength and break (crack) accompanying serratedplastic flow in the tensile stress-strain curves, and that such hightensile strength and serrated plastic flow phenomenon result inexcellent malleability despite the large thickness of the bulk amorphousalloy produced by casting.

[0008] On the bases of the above-described findings of the bulkamorphous alloy production, the inventors of the present invention havecontinued an intensive study to thereby develop a method that is capableof producing a glassy metal material of even larger size with variousconfigurations by a simple procedure. As a consequence, the inventorsproposed a process for producing metallic glass by suction castingwherein an amorphous material of large size having excellent propertiescan be readily produced in simple operation by instantaneously castingthe molten metal material in a mold cooled with water.

[0009] Such process of metallic glass production by suction casting asdisclosed in U.S. Pat. No. 5,740,854 and JP-A 6-249254 is capable ofproducing a columnar bulk amorphous material, and the thus producedcolumnar bulk amorphous material exhibits good properties. In this priorart process, however, the bottom of the water cooled crucible is moveddownward at a high speed and the molten metal is instantaneously castinto a vertically extending water-cooled mold to thereby attain a highmoving speed of the molten metal and a high quenching rate.

[0010] In such production process, the molten metal is fluidized withthe surface of the molten metal becoming wavy, and the surface area ofthe molten metal is increased with the increased surface area contactingthe outer atmosphere. In some extreme cases, the molten metal isfluidized into small separate bulk molten metal droplets before beingcast into the vertically extending mold. Therefore, the surfaces of themolten metal often meet with each other upon casting of the molten metalinto the vertically extending water-cooled mold, and the so called coldshuts or discontinuities are formed at the interfaces of the thus metinterfaces. The resulting bulk amorphous material thus suffered frominferior properties at such cold shuts, and hence, the bulk amorphousmaterial as a whole suffered from poor properties.

[0011] In addition, the metal material is melted in a water-cooledhearth, and the part of the metal in contact with the hearth is at atemperature below the melting point of the metal material even if themetal material is in molten state. The part in contact with the hearth,therefore, is likely to induce nonuniform nucleation. In theabove-described suction casting, such part of the molten metal which mayinduce uniform nucleation is also cast into the vertically extendingwater-cooled mold and there is a fair risk of crystal nucleus formationin the corresponding part.

[0012] Furthermore, since the bottom of the water-cooled crucible ismoved downward at a high speed, the process suffered from a fair chanceof the molten metal entering into the gaps formed between moveable partsand the like to reduce the reproducibility. In some cases, the moltenmaterial entered is even caught in such gaps to result in failure, stop,or incapability of operation.

DISCLOSURE OF INVENTION

[0013] An object of the present invention is to obviate the drawbacks ofthe above-described techniques and to provide processes and apparatusfor producing a metallic glass which is free from the so called coldshuts which are formed by amorphousizing at the interfaces where thesurfaces of the molten metal cooled to a temperature below the meltingpoint by contact with outer atmosphere have met; and which is also freefrom crystalline part where crystal nuclei have developed throughnonuniform nucleation by the molten metal below its melting temperature.In other words, an object of the present invention is to provide asimple process and a simple apparatus for producing a metallic glasswhich are capable of producing a bulk metallic glass of desired shapeexhibiting excellent strength properties in a simple procedure at a highreproducibility by selectively cooling the molten metal above itsmelting temperature at a rate above the critical cooling rate.

[0014] To attain such object, there is provided by the present inventiona process for producing a bulk metallic glass of desired shapecomprising the steps of:

[0015] filling a metal material in a hearth;

[0016] melting said metal material by using a high-energy heat sourcewhich is capable of melting said metal material;

[0017] pressing a molten metal at a temperature above the melting pointof said metal material to deform the molten metal at a temperature abovethe melting point into the desired shape by at least one of compressivestress and shear stress, while avoiding surfaces of the molten metalcooled to a temperature below the melting point of said metal materialfrom meeting with each other during the pressing; and

[0018] cooling said molten metal at a cooling rate higher than thecritical cooling rate of the metal material simultaneously with or aftersaid deformation to produce the bulk metallic glass of desired form.

[0019] According to the present invention, there is also provided by aprocess for producing a bulk metallic glass wherein said molten metal ata temperature above the melting point of said metal material is pressedwhile avoiding not only the meeting of the surfaces of the molten metalcooled to a temperature below the melting point of said metal materialwith each other but also meeting of such molten metal surface withanother surface cooled to a temperature below the melting point of saidmetal material.

[0020] In this process, the pressing and deforming of said molten metalis preferably accomplished by selectively rolling said molten metal at atemperature above the melting point of said metal material into theplate shape or other desired shape with a cooled roll for rolling.

[0021] Preferably, after melting said metal material filled in thehearth, the molten metal at a temperature above the melting point risingover the hearth is selectively rolled with simultaneous cooling byrotating said cooled roll and moving the hearth in relation to said highenergy heat source and said rotating cooled roll to thereby produce ametallic glass of plate shape or other desired shape.

[0022] It is also preferable to use a hearth of an elongated shape, andthe melting, rolling of the molten metal at a temperature above themelting point, and the cooling are continuously conducted by using suchhearth of an elongated shape and moving such hearth in relation to saidhigh energy heat source and said rotating cooled roll to therebycontinuously produce a metallic glass of elongated shape or otherdesired shape.

[0023] The cooled roll for rolling is preferably provided at theposition corresponding the hearth with a molten metal-dischargingmechanism for discharging the molten metal at a temperature higher thanthe melting point from the hearth, said molten metal-dischargingmechanism being fabricated from a material of low thermal conductivity.

[0024] It is also preferable to accomplish the pressing and deforming ofsaid molten metal by selectively transferring said molten metal at atemperature above the melting point of said metal material into a cavityof the desired shape in the mold provided near said hearth withoutfluidizing the molten metal, andpressing the molten metal with a cooledupper mold without delay to forge the molten metal into the desiredshape together with simultaneous cooling.

[0025] In this case, after melting said metal material filled in thehearth, said hearth and said lower mold is preferably moved to rightunderneath said upper mold and the upper mold is descended toward saidlower mold without delay to thereby selectively transfer the moltenmetal at a temperature above the melting point into said mold where itis pressed and cooled to produce the metallic glass of desired shape byforging.

[0026] To attain the above-described object, there is provided by thepresent invention an apparatus for producing a metallic glass comprisinga hearth for accommodating a metal material, a means for melting saidmetal material in said hearth, a means for pressing a molten metal whichhas been melted by said metal material-melting means at a temperaturehigher than the melting temperature to deform the molten metal into thedesired shape by at least one of compressive stress and shear stress,while avoiding the surfaces of the molten metal cooled to a temperaturebelow the melting point of said metal material from meeting with eachother during the pressing; and a means for cooling said molten metal ata cooling rate higher than the critical cooling rate of the metalmaterial simultaneously with or after said deformation by said pressingmeans.

[0027] In this apparatus, said molten metal is preferably pressed whileavoiding not only the meeting of the surfaces of the molten metal cooledto a temperature below the melting point of said metal material witheach other but also meeting of such molten metal surface with anothersurface cooled to a temperature below the melting point of said metalmaterial.

[0028] Preferably, said pressing means doubles as said cooling means.

[0029] Preferably, said pressing means has a cooled roll for rolling anda mold provided near said hearth.

[0030] Preferably, the molten metal at a temperature above the meltingpoint rising over the hearth is cast into said mold by said cooled rollby rotating said cooled roll and moving said hearth and said mold inrelation to said cooled roll and said melting means to accomplish therolling by said cooled roll and said mold.

[0031] Preferably, said hearth is of elongated shape, and the rollingand the cooling by said cooled roll and said mold is continuouslyconducted by moving said hearth and said mold in relation to said cooledroll and said melting means.

[0032] Preferably, said cooled roll for rolling is provided at theposition corresponding said hearth with a molten metal-dischargingmechanism for discharging the molten metal at a temperature higher thanthe melting point from the hearth, said molten metal-dischargingmechanism being fabricated from a material having low thermalconductivity.

[0033] Preferably, said pressing means has a lower mold provided nearsaid hearth into which the molten metal discharged from said hearth isfilled, and an upper mold which forges the molten metal filled in saidlower mold together with said lower mold.

[0034] Preferably, after melting said metal material filled in thehearth, said hearth and said lower mold are moved in relation to saidmelting means and said upper mold until said upper mold is positioned ata position opposing said hearth and said lower mold, and the upper moldis descended or the lower mold is ascended without delay to therebytransfer the molten metal from said hearth into said mold where it isforged.

[0035] Preferably, said upper mold is provided at the positioncorresponding said hearth with a molten metal-discharging mechanism fordischarging the molten metal at a temperature higher than the meltingpoint from the hearth, said molten metal-discharging mechanism beingfabricated from a material having low thermal conductivity.

[0036] The upper mold is preferably provided at the positioncorresponding the hearth with a molten metal-discharging mechanism fordischarging the molten metal at a temperature higher than the meltingpoint from the hearth, said molten metal-discharging mechanism beingfabricated from a material of low thermal conductivity.

[0037] In the present invention, the phrase “meeting” of “the surfacescooled” means the “meeting” of “the surfaces of the molten metal cooledto a temperature below the melting point of said metal material” in anarrower sense. In a broader sense, this phrase also include the casewherein “the surfaces of the molten metal cooled to a temperature belowthe melting point of said metal material” meet with “other surfacescooled to a temperature below the melting point of said metal material”such as the surface of the hearth cooled by water. It should be notedthat the phrase “the surfaces of the molten metal cooled to atemperature below the melting point of said metal material” are thesurfaces of the molten metal cooled to a temperature below the meltingpoint by contact with outer atmosphere, mold, hearth or the like.

[0038] The phrase “pressing a molten metal at a temperature above themelting point of said metal material to deform the molten metal, whileavoiding the surfaces cooled to a temperature below the melting point ofsaid metal material from meeting with each other during the pressing”used herein does not only mean the pouring of the molten metalmaintained at a temperature above the melting point from the cooledhearth into the mold followed by pressing, while avoiding the formationof cold shuts which are formed by the meeting of the surfaces cooled toa temperature below the melting point of said metal material caused byfluidization or surface wave-formation. This phrase also includes use ofa mold fabricated from a material such as quartz which is not thermallydamaged at a temperature above the melting point of the metal material,and heating of the lower mold to a temperature near the melting point,preferably, to a temperature above the melting point, followed bypouring of the metal molten with a high energy source, for example, aradio frequency heat source and maintained at a temperature above themelting point into the preliminarily heated lower mold without formingany surface which is cooled to a temperature below the melting point;and pressing with the cooled upper mold to thereby conduct the pressingand quenching at a rate above the critical cooling rate. Namely, if themetal material used is a material with an extremely low critical coolingrate, the metal molten in a quartz tube may be directly poured andcooled in water while maintaining its shape.

[0039] In other words, the cold shuts are formed when the pressing,deformation, compression, shearing of the molten metal are not conductedat a rate higher than the critical cooling rate and meeting of thecooled surface are not avoided. When a metal having a certain criticalcooling rate, for example, 10° C. /sec is used, an amorphous bulkmaterial without cold shuts can be produced only when the time betweenthe molten state and the deformation and the decrease in temperatureattain the predetermined critical cooling rate (higher than 10° C. /secin this case); and the meeting of the cooled surface is avoided.

[0040] The term “desired shape” used herein is not limited to anyparticular shape as long as the metallic glass material is formedthrough pressing or forging by using an upper press roll or forging moldof various contour and a lower press surface or forging mold of variouscontour which are controlled and cooled in synchronism. Exemplary shapesinclude, a plate, an unspecified profile plate, a cylindrical rod, arectangular rod, and an unspecified profile rod.

BRIEF DESCRIPTION OF DRAWINGS

[0041]FIG. 1 is a flow sheet schematically showing an embodiment of themetallic glass production apparatus of rolling type used in carrying outthe metallic glass production process according to the presentinvention.

[0042]FIG. 2 is a top view of water-cooled hearth and mold used in themetallic glass production apparatus of rolling type shown in FIG. 1.

[0043]FIG. 3 schematically show an embodiment of the production of aplate-shaped amorphous bulk material in the metallic glass productionapparatus of rolling type wherein an arc electrode is used for the heatsource. FIG. 3a is a schematic view of the process wherein the metalmaterial is melted, and FIG. 3b is a schematic view of the processwherein the molten metal is rolled and cooled.

[0044]FIGS. 4a and 4b are partial cross-sectional view and partial topview of essential parts of another embodiment of the metallic glassproduction apparatus of rolling type according to the present invention.

[0045]FIG. 5 is a flow sheet schematically showing an embodiment of themetallic glass production apparatus of forging type used in carrying outthe metallic glass production process according to the presentinvention.

[0046]FIG. 6 schematically show an embodiment of the production of aplate-shaped amorphous bulk material in the metallic glass productionapparatus of forging type wherein an arc electrode is used for the heatsource. FIG. 6a is a schematic view of the process wherein the metalmaterial is melted, and FIG. 6b is a schematic view of the processwherein the molten metal is forged and cooled.

[0047]FIG. 7 is X-ray diffraction pattern for the piece taken from thecentral region of the transverse section of the Zr₅₅Al₁₀Cu₃₀Ni₅ alloymaterial produced in Example 14 of the present invention.

[0048]FIG. 8 is differential scanning calorimetry curve for the piecetaken from the central region of the transverse section of theZr₅₅Al₁₀Cu₃₀Ni₅ alloy material produced in Example 14 of the presentinvention.

[0049]FIG. 9 is a photomicrograph showing the metal structure in thecentral region of the transverse section of the Zr₅₅Al₁₀Cu₃₀Ni₅ alloymaterial produced in Example 14 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0050] The processes and the apparatus for producing metallic glass ofthe present invention are described in detail by referring to thepreferred embodiments shown in the attached drawings.

[0051] In the metallic glass production process of the presentinvention, a hearth, for example, a water-cooled copper hearth in theform of a recess is filled with a metal material which is preferably amixture of a powder or pellets of metals having high amorphousizingproperties. Next, the metal material is melted by means of a high energyheat source, for example, by an arc heat source after evacuating thechamber and maintaining the vacuum, or under reduced pressure, or aftersubstituting the chamber with an inert gas with or without forcedcooling of the hearth. (Melting in vacuum has the merit of retardedcooling of the molten metal due to the absence of convection compared tothe casting at atmospheric pressure. The metal may be melted, forexample, by means of electron beam.)

[0052] Next, the molten metal at a temperature above the melting pointof the metal material is transferred into the cavity of the mold. Moreillustratively, in the case of the water-cooled hearth, the molten metalat a temperature above the melting point is selectively transferred intothe mold cavity by directly pressing the molten metal in the hearth witha new mold or by transferring the molten metal mass into the mold cavityfollowed by pressing. In such transfer of the molten metal onto the moldcavity, the surfaces of the molten metal in contact with the atmosphereshould be avoided from meeting with each other, and fluidization orsurface weaving of the molten metal should be avoided. When the moltenmetal is pressed in the mold cavity, at least one of compression stressand shear stress is applied to the molten metal at a temperature higherthan the melting temperature for deformation of the molten metal intothe desired shape, and the molten metal at a temperature higher than themelting temperature is cooled at a rate higher than the critical coolingrate of the metal material after the deformation or simultaneously withthe deformation.

[0053] For example, in an embodiment, the molten metal at a temperatureabove the melting point rising over the hearth is selectively rolledsimultaneously with cooling into an ingot of plate shape or otherdesired shape by means of a cooled (water-cooled) roll for (metal)rolling disposed on the hearth (this process is referred to as (metal)rolling process). In this process, the hearth is moved in relation tothe cooled roll for rolling which is rotated. When a hearth of anelongated shape is used, the metal material in the hearth may be meltedin continuity by the high energy heat source in correspondence with therelative movement of the hearth, and the continuously melted metal at atemperature higher than the melting point is continuously rolled andcooled by the continuously rotating cooled roll for rolling to producean ingot of plate shape or other desired shape. It should be noted thatthe cooled roll for rolling is preferably provided with a moltenmetal-discharging mechanism fabricated from a material of low thermalconductivity at the position corresponding the hearth to therebydischarge the molten metal at a temperature higher than the meltingpoint from the hearth into the new mold surface (rolling surface).

[0054] In another embodiment, the molten metal in the hearth at atemperature higher than the melting point of the metal material isselectively transferred into the lower half of the mold having a cavityof desired shape provided near the hearth without causing fluidizationor surface weaving of the molten metal, and the molten metal isimmediately pressed with the cooled upper half of the mold which mateswith the cavity of the lower mold for press forging of the molten metal,or alternatively, the mold may be cooled simultaneously with the forging(this process is hereinafter referred to as forging process). In thisprocess, the hearth and the lower mold are moved in relation to the highenergy heat source and the upper mold to align the lower and the uppermolds, and the lower and the upper molds are mated by either descendingthe upper mold or ascending the lower mold to press forge the moltenmetal in the lower mold at a temperature above the melting pointsimultaneously with the rapid cooling of the mold. It should be notedthat the upper mold is preferably provided with a moltenmetal-discharging mechanism fabricated from a material of low thermalconductivity at the position corresponding the hearth to therebydischarge the molten metal at a temperature higher than the meltingpoint from the hearth into the cavity of the lower mold.

[0055] As mentioned above, the first object of the present invention isto produce a bulk amorphous material of the desired final shape which isfree from cold shuts, and hence, which is free from casting defects; andthe second object is, in addition to the fist object, to produce a bulkamorphous material which is free from crystal nuclei resulting from thenonuniform nucleation. Therefore, the means for attaining such objectsare not limited to the above-described processes, and any means can beadopted as long as the molten metal as a mass at a temperature above themelting point can be selectively formed into the final desired shape bydirecting compression stress and/or shear stress to the molten metal bypressing the molten metal while avoiding the meeting of the surfaces ofthe molten metal which had been in contact with the atmosphere byfluidization or surface weaving of the molten metal or the meeting ofthe preceding molten metal stream with the subsequent molten metalstream.

[0056] For example, most preferable means are use of a levitation deviceor the like wherein the metal material is melted and maintained at atemperature above the melting point in non-contacted state, and the useof cold crucible (skull melting) device or the like wherein the metalmaterial is melted and maintained at a temperature above the meltingpoint in a state resembling the non-contacted state. Sections of asectional die, for example, two sections of a mold are moved toward themolten metal maintained at a temperature above the melting point innon-contacted state or in a state resembling the non-contacted state tothereby sandwich and press the molten metal into the desired finalshape. In an alternative process, a material which does not melt at atemperature higher than the melting point of the metal material, whichdoes not react with the molten metal, and which has excellent mechanicalstrength or a material which is not damaged by high temperature heatingand rapid cooling is chosen in accordance with the type of the moltenmetal from such materials as carbon, nickel, tungsten, ceramics, and thelike, and the lower half of the mold is fabricated from the thusselected material. The metal material is filled in the lower mold,melted, and pressed with the upper mold immediately after the melting ofthe metal material for press forming. Simultaneously with the pressing,the upper and lower molds may be cooled with a coolant such as a gas orwater to produce the bulk amorphous material of desired final shape. Insuch a case, it is preferable that the lower mold is not cooled duringthe melting of the metal and the cooling of the lower mold is preferablystarted after the completion of the melting, and in such a case, thelower mold may be fabricated from any material as long as the lower moldcan maintain the temperature near the melting point. For example, thelower mold may be fabricated from either a material of high conductivityor a material of low conductivity.

[0057] It should also be noted that, in the metal rolling process asdescribed above, the metal rolling may be conducted by two-roll metalrolling process which is capable of producing a bulk amorphous materialhaving desired surface pattern. In a single roll metal rolling process,the rolling and the cooling by the cooled roll for metal rolling may beaccomplished not only by the reciprocal movement of the hearth in onedirection but the hearth may be rotated within the horizontal plane sothat the roll may be moved in different directions. In the forgingprocess, the hearth and the lower mold may be rotated within thehorizontal plane in addition to their reciprocal movement in onedirection.

[0058] A bulk amorphous material of plate shape or other shape, namely,a large sized metallic glass bulk material is thus produced. The largesized metallic glass bulk material thus produced which has notexperienced nonuniform solidification is a high density bulk amorphousmaterial which is free from cold shuts and other casting defects, whichis free from crystal nuclei resulting from nonuniform nucleation, andwhich has uniform strength properties, in particular, impact strength.Furthermore, the large sized metallic glass bulk material thus producedhas been produced at once into the final desired shape adapted for itsuse, and no further processing is required.

[0059] When a metal material is melted in a metallic hearth, inparticular, in a water-cooled copper hearth to obtain the molten metalat a temperature above the melting point of the metal material, the partof the molten metal in contact with the hearth is inevitably cooled to atemperature below the melting temperature, and nonuniform nucleation isinduced by this part of the molten metal where crystal nuclei arepresent. The resulting bulk material, therefore, is likely to be a bulkamorphous material wherein crystalline phase is present. Even if thecrystalline phase were present in the bulk amorphous material, thematerial can be used as a functional material having both thefunctionality of the amorphous phase and the functionality of thecrystalline phase, namely, as a functionally gradient material as longas the material is sufficiently functional and free from cold shuts andother casting defects. Such functionally gradient material is alsowithin the scope of the amorphous bulk material produced by the presentinvention.

[0060] The present invention may be applied for the alloys of almost anycombination of the elements including the above mentioned ternaryalloys, Zr based alloys such as Zr—Al—Ni—Cu, Zr—Ti—Al—Ni—Cu,Zr—Nb—Al—Ni—Cu, and Zr—Al—Ni—Cu—Pd alloys and other multi-componentalloys comprising four or more components to form the amorphous phase,as long as these alloys can be melted using high energy heat source suchas the arc heat source. When such alloys are used for the metal materialof the invention, it would be preferable to use the alloy in powder orpellet form to facilitate rapid melting of the alloy by high energy heatsource. The form of the alloy, however, is not limited to such forms,and the metal material used may be in any form as long as rapid meltingis possible. Exemplary forms other than powder and pellets include wire,ribbon, rod, and ingot, and a metal material of any desired form may beadequately selected depending on the hearth, particularly thewater-cooled hearth and the high-energy heat source employed.

[0061] The high-energy heat source used in the present invention is notlimited to any particular type, and any heat source may be employed solong as it is capable of melting the metal material filled in the hearthor the water-cooled hearth. Typical high-energy heat sources include archeat source, plasma heat source, electron beam, and laser. When suchheat source is employed, either single heat source or multiple heatsources may be provided per one hearth or one water-cooled hearth.

[0062] The basic constitutions of the process and the apparatus forproducing a metallic glass of the present invention are as describedabove. Next, the apparatus for producing metallic glass of the presentinvention embodying the present process are described.

[0063]FIG. 1 is a flow sheet schematically showing an embodiment of themetallic glass production apparatus of metal rolling type used incarrying out the metallic glass production process according to thepresent invention.

[0064] As shown in FIG. 1, the metallic glass production apparatus ofrolling type 10 comprises a water-cooled copper hearth (hereafterreferred to as a water-cooled hearth) 12 having a recess ofpredetermined configuration into which the metal material, for example,a metal material in powder or pellet form is to be filled; a rollcasting section 13 extending from the periphery of the water-cooledhearth 12; a water-cooled electrode (tungsten electrode) 14 for arcmelting the metal material in the water-cooled hearth 12; and awater-cooled roll for rolling 16 for rolling the molten metal arc-meltedat a temperature higher than the melting point rising from thewater-cooled hearth 12 onto the roll casting section 13 to form an ingotof plate shape, and which rapidly cools the metal material at a ratehigher than the critical cooling rate intrinsic to the metal material(molten metal) simultaneously with the rolling; a cooling water supplier18 for supplying a cooling water to the water-cooled hearth 12, thewater-cooled electrodes 14, and the water-cooled roll for rolling 16 bywater circulation; a vacuum chamber 20 for accommodating thewater-cooled hearth 12, the water-cooled electrodes 14, and thewater-cooled roll for rolling 16; and a hearth-moving mechanism 22 formoving the water cooled hearth 12 provided with the roll casting section13 in vacuum chamber 20 in the direction of arrow b (in horizontaldirection) in synchronism with the rotation of the water-cooled roll forrolling 16 in the direction of arrow a.

[0065] The water-cooled roll for rolling 16 is rotated by a drive motor17 to selectively roll and rapidly cool the molten metal at atemperature higher than the melting point rising from the water-cooledhearth 12 between the roll casting section 13 and the water-cooled rollfor rolling 16, and the hearth-moving mechanism 22 is constructed so asto be driven by a drive motor 23 to horizontally move the water-cooledhearth 12 in synchronism with the rotation of the water-cooled roll forrolling 16. Although the water-cooled roll for rolling 16 is rotated bydrive motor 17 in the embodiment of FIG. 1, the embodiment shown in FIG.1 is not a sole case and the present invention may be rotated by amechanism other than such mechanism. For example, the water-cooled rollfor rolling 16 may be kept in pressure contact with the water-cooledhearth 12 by means of a biasing means (not shown) such as a spring whichcan control the pressure, and the water-cooled roll for rolling 16 maybe rotated by means of the friction between the water-cooled roll forrolling 16 and the water-cooled hearth 12 in correspondence to thehorizontal movement of the water-cooled hearth 12 by the hearth-movingmechanism 22. The water-cooled electrodes 14 is connected to an arcpower source 24. The water-cooled electrodes 14 is arranged at a slightangle from the direction of the depth of the recess 12 a of thewater-cooled hearth 12, and the electrodes 14 is arranged to enable itscontrol in X, Y and Z directions by a stepping motor 15. In order tokeep the gap (in Z direction) between the metal material in thewater-cooled hearth 12 and the water-cooled electrodes 14 at a constantdistance, the position of the metal material may be detected by asemiconductor laser sensor 26 to automatically control the movement ofthe water-cooled electrodes 14 by the motor 15. When the gap between thearc electrodes 14 and the metal material is inconsistent, the arcestablished would be unstable, leading to inconsistency in the melttemperature. A nozzle for discharging a cooling gas (for example, argongas) may be provided near the arc generation site of the water-cooledelectrode 14 to discharge the cooling gas supplied from a gas source (asteel gas cylinder) 28 to thereby promote rapid cooling of the moltenmetal after the heat melting.

[0066] The vacuum chamber 20 has the structure of water-cooling jacketmade from an SUS stainless steel, and is connected to an oil diffusionvacuum pump (diffusion pump) 30 and oil rotary vacuum pump (rotary pump)32 by means of the exhaust port for evacuation. The vacuum chamber 20has an argon gas inlet port in communication with a gas source (a steelgas cylinder) 34 to enable purging of the atmosphere with the inert gasafter drawing a vacuum. The cooling water supplier 18 cools the coolingwater that has circulated back by means of a coolant, and then send thethus cooled cooling water to the water-cooled hearth 12, thewater-cooled electrode 14, and the water-cooled roll for rolling 16.

[0067] The hearth-moving mechanism 22 which moves the water-cooledhearth 12 in the (horizontal) direction shown by arrow b in FIG. 1 isnot limited to any particular mechanism, and any mechanism known in theart for translational or reciprocal movement may be employed, forexample, a drive screw and a traveling nut using a ball thread,pneumatic mechanism such as air cylinder, and hydraulic mechanism suchas hydraulic cylinder.

[0068] Next, the process for producing a metallic glass by the rollingsystem according to the present invention is described by referring toFIGS. 1, 2 and 3.

[0069]FIG. 2 is a schematic top view of the water-cooled hearth and theroll casting mold section (the mold for rolling) 13 shown in FIG. 1.FIG. 3a is a schematic cross sectional view of the metalmaterial-melting step in the production process of a plate shapedamorphous bulk material in the metallic glass production apparatus ofrolling type wherein arc melting is employed. FIG. 3b is a schematiccross-sectional view of the step wherein the molten metal is rolled andcooled by the water-cooled roll for rolling 16 and the roll casting moldsection 13 of water-cooled hearth 12.

[0070] First, the water-cooled roll for rolling 16 is rotated by thedrive motor 17, and the hearth-moving mechanism 22 is driven by thedrive motor 23 in synchronism with the rotation of the water-cooled rollfor rolling 16 to move the water-cooled hearth 12 to the initialposition where it is set as shown in FIG. 3a. The metal material(powder, pellets, crystals) is then filled in the recess 12 a of thewater-cooled hearth 12. In the meanwhile, the position of thewater-cooled electrode 14 is adjusted in X, Y and Z directions by meansof the sensor 26 and the motor 15 via an adapter 14 a (see FIGS. 3a and3 b) and the distance between the water-cooled electrode 14 and themetal material (in Z direction) is adjusted to a predetermined distance.

[0071] The chamber 20 is then evacuated by the diffusion pump 30 and therotary pump 32 to a high vacuum of, for example, 5×10⁻⁴ Pa (using liquidnitrogen trap), and argon gas is supplied to the chamber 20 from theargon gas source 34 to purge the chamber 20 with argon gas. In themeanwhile, the water-cooled hearth 12, the water-cooled electrode 14,and the water-cooled roll for rolling 16 are cooled by the cooling watersupplied from the cooling water supplier 18.

[0072] When the preparation as described above is completed, the arcpower source 24 is turned on to generate a plasma arc 36 between the tipof the water-cooled electrode 14 and the metal material to completelymelt the metal material to form the molten alloy 38 (see FIG. 3a). Theark power source 22 is then turned off to extinguish the plasma ark 36.Simultaneously, the drive motors 17 and 23 are turned on to horizontallymove the water-cooled hearth 12 by the hearth-moving mechanism 22 in thedirection of the arrow b as shown in FIG. 3b at the predetermined rate,and rotate the water-cooled roll for rolling 16 at a constant rotationrate in synchronism with the horizontal movement of the water-cooledhearth 12 in the direction of the arrow a. The molten metal at atemperature above the melting point rising over the water-cooled hearth12 is thus selectively transferred into the cavity (recess) 13 a in theroll casting mold section 13 of the water-cooled hearth 12 by thewater-cooled roll for rolling 16, and the thus transferred metal in themold cavity 13 a is rolled and pressed by sandwiching and pressing themolten metal between the roll casting section 13 and the water-cooledroll for rolling 16 at a predetermined pressure with simultaneouscooling. The metal liquid (molten metal) 38 is thus rolled by thewater-cooled roll for rolling 16 into a thin plate simultaneously withthe cooling, and therefore, the molten metal is cooled at a high coolingrate. Since the molten metal 38 is cooled at a rate higher than thecritical cooling rate while it is rolled into its final plate-likeshape, the molten metal undergoes a rapid solidification to become theamorphous bulk material 39 of the final desired plate shape in the rollcasting mold section 13.

[0073] The thus obtained amorphous bulk material 39 in the form of aplate is the one which has been selectively formed from the molten metalat a temperature above the melting point of the metal material(preferably, the molten metal of the part of the molten metal risingover the water-cooled hearth 12 which is at a temperature above themelting point) which is completely free from the portion 37 of themolten metal in the vicinity of the bottom of the water-cooled hearth 12whose temperature is lower than the melting point of the metal materialand which is likely to invite nonuniform nucleation, and hence formationof the crystalline phase. In addition, the plate shaped amorphous bulkmaterial 39 is the one formed from the molten metal at once into thefinal plate form with simultaneous cooling, without causing anyfluidization or surface weaving. Therefore, the molten metal isuniformly cooled and solidified, and the resulting bulk material 39 isfree from the crystalline phase resulting from the nonuniformsolidification or nonuniform nucleation as well as the casting defectssuch as cold shuts.

[0074] In the embodiment shown in FIGS. 3a and 3 b, the portion 37 ofthe molten metal in the vicinity of the bottom of the water-cooledhearth 12 whose temperature is lower than the melting point is avoidedfrom entering into the final product, and a plate-shaped amorphous bulkmaterial 39 of high strength is reliably produced. In this embodiment,however, some of the molten metal 38 whose temperature is above themelting temperature of the metal material remains within the recess 12 aof the water-cooled hearth 12, and such molten metal 38 is not used inthe production of the plate-shaped amorphous bulk material 39,detracting from efficiency. Therefore, in an alternate embodiment of thepresent invention, as shown in FIG. 4a the water-cooled roll for rolling16 is provided with a molten metal-discharging mechanism 16 a in theform of a protrusion fabricated from a material of low thermalconductivity at the position corresponding the recess 12 a of thewater-cooled hearth 12 to thereby selectively discharge the molten metalat a temperature higher than the melting point from the recess 12 a andprevent nonuniform nucleation. The molten metal 38 in the water-cooledhearth 12 at a temperature above the melting point is therebyefficiently utilized. In such embodiment, the protrusion constitutingthe molten metal-discharging mechanism 16 a is preliminarily heated to atemperature near the melting temperature of the molten metal.

[0075] As shown in FIG. 4(b), when the water-cooled hearth 12 (namely,the recess 12 a) comprises an elongated recess 12 a (of semicylindricalconfiguration), and the roll casting mold section 13 having the cavity13 a is provided on either side or both sides of the hearth 12, themetal material in the water-cooled hearth 12 may be continuously meltedby the water-cooled electrode 14, and the molten metal at a temperatureabove the melting point may be selectively transferred by thewater-cooled roll for rolling 16 into the cavity 13 a of the rollcasting mold section 13 of the water-cooled hearth 12 for continuousrolling with simultaneous cooling. As in the case of FIG. 4(a), thewater-cooled roll for rolling 16 of this embodiment may be provided witha molten metal-discharging mechanism 16 a, for instance, on itsperiphery with a molten metal-discharging mechanism 6 a in the form of aridge of a predetermined length to selectively and effectively dischargethe molten metal at a temperature higher than the melting point in thewater-cooled hearth 12 to the cavity 13 a and prevent nonuniformnucleation. As described above, the molten metal-discharging mechanism16 a in the form of a ridge is preferably fabricated from a material oflow thermal conductivity, and more preferably, the moltenmetal-discharging mechanism 16 a is preliminarily heated to atemperature near the melting temperature of the molten metal.

[0076] In the metallic glass production process of the rolling typeaccording to the present invention, the roll casting mold section 13 isformed integrally with the water-cooled hearth 12. Instead of the rollcasting mold section 13 integrally formed with the water-cooled hearth12, another roll for rolling may be provided underneath the water-cooledroll for rolling 16 to constitute a twin-roll rolling system. In such acase, the cross section of the plate-shaped amorphous bulk materialproduced by the rolling may be changed by changing the contour of thelower roll, for example, the contour of the cavity, into various shapenot restricted to the rectangle shape.

[0077] In the embodiment as described above, the water-cooled roll forrolling 16 rotates with its axis of rotation remaining in the sameposition, and the position in the horizontal plane of the water-cooledelectrode 14 is also substantially fixed. It is the water-cooled hearth12 that is moved within its horizontal plane. The present invention isnot limited to such an embodiment, and alternatively, the rotatingwater-cooled roll for rolling 16 and the water-cooled electrode 14 maybe moved in parallel with each other in horizontal direction, and thewater-cooled hearth 12 may be the fixed at one position.

[0078] Although the roll casting mold section 13 integrally formed withthe water-cooled hearth 12 may be formed with a cavity 13 a as shown inthe drawing, and the lower roller of the twin-roll system may be alsoformed with the cavity 13 a, the present invention is not limited tosuch types and the provision of the cavity is not always necessary aslong as the molten metal 38 is adequately rolled.

[0079] In the embodiments as described above, the water-cooled roll forrolling 16 is strongly water cooled, and the roll casting mold section13 and the lower roller of the twin-rolling system are not forcedlycooled. It is of course possible to forcedly cool the roll casting moldsection 13 and the lower roller of the twin-rolling system. In addition,the water-cooled hearth 12, the water-cooled electrode 14 and thewater-cooled roll for rolling 16 are forcedly cooled by cooling water.The present invention is not limited to such embodiment, and othercooling media (coolant) such as a coolant gas may be used.

[0080] The metallic glass production process of rolling type and theapparatus used therefor of the present invention are basically asdescribed above.

[0081] Next, the process for producing a metallic glass by the forgingtype as well as the apparatus used therefor according to the presentinvention is described in detail.

[0082]FIG. 5 is a flow sheet schematically showing an embodiment of themetallic glass production apparatus of forging type used in carrying outthe metallic glass production process according to the presentinvention.

[0083] As shown in FIG. 5, the metallic glass production apparatus offorging type 50 is similar to the metallic glass production apparatus ofrolling type 10 in FIG. 1 except that the molten metal at a temperatureabove the melting point is press formed (forged, or cast forged) betweenthe lower mold 52 provided near the water cooled hearth 12 and therapidly cooled upper mold 54 instead of the roll casting mold section 13integrally formed with the water cooled hearth 12 and the water-cooledroll for rolling 16. Same reference numerals are used for the elementscommon to the apparatus 50 and the apparatus 10, and the explanation isomitted.

[0084] As shown in FIG. 5, the metallic glass production apparatus offorging type 50 comprises a water-cooled hearth 12; a water-cooledelectrode 14; a lower mold 52 having a cavity 52 a having the desiredfinal configuration provided near the water-cooled hearth 12; a moltenmetal-discharging mechanism 54 for discharging the molten metal at atemperature higher than the melting point from the water-cooled hearth12 into the cavity 52 a of the lower mold 52, while avoidingnonuniformnucleation; an upper mold 54 which mates with the cavity 52 aof the lower mold 52 to press mold (forge) the molten metal in thecavity 52 a at a temperature above the melting point with simultaneousquenching of the molten metal at a rate higher than the critical coolingrate intrinsic to the metal material (molten metal); a cooling watersupplier 18 for supplying a cooling water to the water-cooled hearth 12,the water-cooled electrodes 14, and the upper mold 54 by watercirculation; a vacuum chamber 20 for accommodating the water-cooledhearth 12, the water-cooled electrodes 14, and the upper mold 54; ahearth-moving mechanism 22 for moving the water cooled hearth 12integrally formed with the lower mold 52 in vacuum chamber 20 in thedirection of arrow b (in horizontal direction) in order that theposition of the lower mold 52 is set just below the upper mold 54; andan upper mold-moving mechanism 56 for moving the upper mold 54 in thedirection of arrow (in vertical direction) in the vacuum chamber 20 tothereby selectively discharge the molten metal at a temperature abovethe melting point in the water-cooled hearth 12 (integrally formed withthe lower mold 52 which has been moved to the position of press molding)into the cavity 52 a of the lower mold 52 by means of the moltenmetal-discharging mechanism 54 a provided with the upper mold 54, andselectively press mold (forge) the molten metal at a temperature abovethe melting point in the cavity 52 a simultaneously with quenching. Theupper mold-moving mechanism 56 for vertical movement of the upper mold54 is driven by the drive motor 57.

[0085] Next, the process for producing a metallic glass by the forgingtype according to the present invention is described by referring toFIGS. 5 and 6.

[0086]FIG. 6a is a schematic cross sectional view of the metalmaterial-melting step wherein in the process wherein an amorphous bulkmaterial of the desired final shape is produced in the metallic glassproduction apparatus of forging type wherein arc melting is employed.FIG. 6b is a schematic cross-sectional view of the step wherein themolten metal is forged and cooled between the upper mold 54 and thelower mold 52 integrally formed with the water-cooled hearth 12.

[0087] In the metallic glass production apparatus of forging type 50,the upper mold-moving mechanism 56 and the hearth-moving mechanism 22are respectively driven by the drive motors 57 and 23 to move thewater-cooled hearth 12 integrally formed with the lower mold 52 and theupper mold 54 to the initial position where there are set as shown inFIG. 6a. As in the case of the metallic glass production apparatus ofrolling type 10, the metal material is then filled in the recess 12 a ofthe water-cooled hearth 12, whereby the preparation for the metallicglass production by forging is completed.

[0088] After the completion of such preparation, the arc power source 24is turned on as in the case of the metallic glass production apparatusof rolling type 10 to generate a plasma arc 36 between the tip of thewater-cooled electrode 14 and the metal material to completely melt themetal material to form the molten alloy 38 (see FIG. 6a). The ark powersource 24 is then turned off to extinguish the plasma arc 36.Simultaneously, the drive motor 23 is turned on to horizontally move thewater-cooled hearth 12 at a constant speed by the hearth-movingmechanism 22 in the direction of arrow b to the position just below theupper mold 54 shown in FIG. 6b. In the meanwhile, the dive motor 57 isturned on to descend the upper mold 54 in the direction of the arrow cby the upper mold-driving mechanism 56.

[0089] As the upper mold 54 descends, the molten metal-dischargingmechanism 54 a selectively discharges the molten metal at a temperatureabove the melting point from the water-cooled hearth 12 and the thusdischarged molten metal is forcedly pressed into the cavity 52 a of thedesired final shape in the lower mold 52 integrally formed with thewater-cooled hearth 12. The molten metal discharged by the moltenmetal-discharging mechanism 54 a from the water-cooled hearth 12 andforcedly pressed into the cavity 52 a is completely free from theportion 37 of the molten metal in the vicinity of the bottom of thewater-cooled hearth 12 whose temperature is lower than the melting pointof the metal material and which is likely to invite nonuniformnucleation, and hence, formation of the crystalline phase, and thedefect such as nonuniform nucleation of the amorphous bulk material canbe prevented. It should be noted that the molten metal-dischargingmechanism 54 a in the form of a protrusion or ridge is preferablyfabricated from a material of low thermal conductivity, and morepreferably, the molten metal-discharging mechanism 54 a is preliminarilyheated to a temperature near the melting temperature of the moltenmetal.

[0090] The upper mold 54 continues to descend and meets with the lowermold 52, and the upper mold 54 mates with the cavity 52 a of the lowermold 52. The molten metal at a temperature above the melting point inthe cavity 52 a is thereby press molded as it is sandwiched between theupper and lower molds 54 and 52 at a predetermined pressure. In otherwords, the molten metal is forged by compression stress simultaneouslywith the rapid cooling by the water-cooled upper mold 54. The metalliquid (molten metal) 38 is thus press molded (forged) into the desiredfinal shape by the upper and lower molds 54 and 52 together with thecooling, and a high cooling rate of the molten metal is therebyrealized. Since the molten metal 38 is cooled at a rate higher than thecritical cooling rate while it is press molded (forged) into its finalplate shape, the molten metal undergoes rapid solidification to becomethe amorphous bulk material 39 of the final desired thin plate shape.

[0091] The thus obtained amorphous bulk material 39 in the form of aplate is the one which has been selectively formed from the molten metalat a temperature above the melting point of the metal material which iscompletely free from the portion 37 of the molten metal in the vicinityof the bottom of the water-cooled hearth 12 whose temperature is lowerthan the melting point of the metal material, and which is likely toinvite nonuniform nucleation, and hence formation of the crystallinephase. In addition, the plate shaped amorphous bulk material 39 is theone formed from the molten metal at once into the final plate form withsimultaneous cooling, without causing any fluidization or surfaceweaving. Therefore, the molten metal is uniformly cooled and solidified,and the resulting bulk material 39 is free from the crystalline phaseresulting from the nonuniform solidification or nonuniform nucleation aswell as the casting defects such as cold shuts.

[0092] In the embodiment as described above, the position in thehorizontal plane of the water-cooled electrode 14 and the upper mold 54are substantially fixed, and it is the water-cooled hearth 12 that ismoved within its horizontal plane. The present invention is not limitedto such an embodiment, and alternatively, the water-cooled electrode 14and the upper mold 54 may be moved in parallel with each other inhorizontal direction, and the water-cooled hearth 12 may be the fixed atone position. In the embodiment as described above, the horizontallymoved water-cooled hearth 12 is provided with only one pair of thewater-cooled hearth 12 and the lower mold 52. The present invention isnot limited to such an embodiment, and two or more pairs of the hearth12 and the lower mold 52 may be radially arranged at a predeterminedinterval on a rotatable disk so that the rotatable disk may beincrementally rotated. A continuous forging system of rotatable disktype is thereby constituted to enable successive forging one afteranother by incremental rotation of the rotatable disk. Of cause, therotatable disk may be provided with only one pair of the water-cooledhearth 12 and the lower mold 52, and the one or more pair of thewater-cooled hearth 12 and the lower mold 52 may be provided not only onthe rotatable disc but also on a plate of other configuration such as arectangular plate as long as the pairs of the water-cooled hearth 12 andthe lower mold 52 can be arranged on the plate and the plate isrotatable.

[0093] In the embodiments as described above, the upper mold 54 isstrongly water cooled, and the lower mold 52 and the like are notforcedly cooled. It is of course possible to forcedly cool the lowermold 52 and the like. In addition, the water-cooled hearth 12, thewater-cooled electrode 14 and the upper mold 54 are forcedly cooled bycooling water. The present invention is not limited to such embodiment,and other cooling media (coolant) such as a coolant gas may be used.

[0094] The upper mold-moving mechanism 56 which presses the upper mold54 onto the lower mold 52 is not limited to any particular mechanism,and any mechanism known in the art, for example, a hydraulic orpneumatic mechanism may be employed.

[0095] The metallic glass production process of forging type and theapparatus used therefor of the present invention are basicallyconstructed as described above.

[0096] Industrial Applicability

[0097] As described above, the present invention has enabled productionof a bulk amorphous material which is free from casting defects such ascold shuts and which has excellent strength properties. This productionprocesses and apparatus are highly reproducible, and are capable ofproducing a bulk amorphous material of desired final shape in simplesteps. The product produced by the present invention is also free fromcrystalline phase formed by the development of the crystal nucleithrough nonuniform nucleation. Accordingly, the process and theapparatus of the present invention, wherein the molten metal at atemperature above the melting point is selectively cooled at a ratehigher than the critical cooling rate, are capable of producing the bulkamorphous material of desired shape comprising single amorphous phasehaving excellent strength properties in simple steps at a highreproducibility.

[0098] Next, the metallic glass production process and apparatusaccording to the present invention are described in greater detail byreferring to the Examples.

EXAMPLES Examples 1 to 14

[0099] The metallic glass production apparatus of forging type 50 shownin FIGS. 5 and 6 was used to produce amorphous bulk material alloys ofrectangular plate with various dimensions in the range of 100 mm(length)×30 mm (width)×2 to 20 mm (thickness) from the 14 alloys shownin Table 1.

[0100] In the Examples, the water-cooled copper hearth 12 was asemispherical recess with a dimension of 30 mm (diam.)×4 mm (depth), andthe cavity 52 a of the lower mold 52 was a rectangular recess with adimension of 21 mm (length)×30 mm (width)×2 mm (depth).

[0101] The water-cooled electrode 14 used was the one which is capableof fully utilizing the arc heat source of 3,000° C. and controlling thetemperature by means of an IC cylister. The argon gas for cooling wasinjected from a cooling gas-injection port (not shown) provided on theadapter 14 a. The water-cooled electrode 14 had an arc generating sitecomprising thorium-containing tungsten, and therefore, electrodeconsumption and contamination was minimized. The electrode 14 also had awater-cooled structure which mechanically and thermally enabled stable,continuous operation at a high thermal efficiency.

[0102] In these Examples, the metallic glass production apparatus offorging type 50 was operated by the conditions as described below. Theelectric current and the voltage employed for the arc melting were 250 Aand 20 V, respectively. The gap between the water-cooled electrode 14and the metal material in the form of a powder or pellets was adjustedto 0.7 mm. The pressure applied to the upper mold 54 for the pressmolding was in the range of 5 M to 20 MPa.

[0103] The rectangular amorphous alloy plates produced by the forgingprocess as described above were examined for their structure by X-raydiffractometry, optical microscopy (OM), scanning electron microscopycombined with energy diffusion X-ray spectroscopy (EDX). The samples foruse in the optical microscopy (OM) were subjected to an etchingtreatment in 30% hydrofluoric acid solution at 303 K for 1.8 ks. Thesamples were also evaluated for their structural relaxation, glasstransition temperature (Tg), crystallization temperature (Tx), and heatof crystallization (ΔHx: temperature range of the supercooled liquidregion) by differential scanning calorimetry (DSC) at a heating rate of0.67 K/s. The rectangular amorphous alloy plate samples were alsoevaluated for mechanical properties. The mechanical properties evaluatedwere tear energy (Es), Vickers hardness (Hv), tensile strength (σf)(tensile strength could not be measured for the Examples 4, 5, 10 and11, and compression strength was measured), elongation (εf), and Young'smodulus (E). The Vickers hardness (Hv) was measured by Vickersmicrohardness tester at a load of 100 g.

[0104] The alloy composition of the 14 alloys used for the production ofthe rectangular amorphous alloy plates are shown in Table 1 togetherwith the properties of the rectangular amorphous alloy plates. It shouldbe noted that “t” in Table 1 stands for the thickness of the rectangularamorphous alloy plates. TABLE 1 Example Alloy Es t Tg TX ΔTX δf εf E No.Composition (kJ/m³) (mm) (K) (K) (K) Hv (MPa) (%) (GPa) 1Zr_(62 · 5)Al_(7 · 5)Cu₂₀ 66 8 623 750 127 510 1730 2.0 86 2Zr₅₇Ti₃Al₁₀Ni₁₀Cu₂₀ 59 5 655 740 85 540 1800 1.8 88 3 Zr₆₀Al₁₀Cu₃₀ 67 5620 708 88 490 1650 3.1 77 4 Fe₅₆Cu₇Ni₇Zr₁₀B₂₀ — 4 810 883 73 1250 *3560 1.8 160 5 Fe₅₆Cu₇Ni₇Zr₂Nb₈B₂₀ — 3 805 892 87 1290 * 3630 2.0 167 6Mg₇₅Cu₁₅Y₁₀ — 5 424 471 47 250 880 1.9 47 7 Mg₇₀Ni₂₀La₁₀ — 5 470 503 33300 900 2.1 50 8 La₆₅Al₁₅Ni₂₀ — 5 180 240 60 370 1210 2.0 58 9La₆₅Al₁₅Cu₂₀ — 5 175 233 58 355 1120 2.2 56 10 Co₅₆Fe₁₄Zr₁₀B₂₀ — 2 810838 28 1050 * 2850 1.7 150 11 Co₅₁Fe₂₁Zr₈B₂₀ — 2 800 884 84 1080 * 30101.8 153 12 La₅₅Al₁₅Ni₁₀Cu₂₀ 72 7 210 288 78 360 1150 2.2 56 13Pd₄₀Cu₃₀Ni₁₀P₂₀ 70 15 580 678 98 550 1760 2.7 78 14 Zr₅₅Al₁₀Cu₃₀Ni₅ 6820 680 760 80 540 1680 2.2 85

[0105] The results of the X-ray diffractometry, measurements of heat ofcrystallization, photomicrograph (×500) for the Zr₅₅Al₁₀Cu₃₀Ni₁₅ alloymaterial produced in Example 14 are shown in FIGS. 7, 8 and 9,respectively.

[0106]FIG. 7 represents X-ray diffraction patterns of theZr₅₅Al₁₀Cu₃₀Ni₁₅ alloy material produced in Example 14 for the centralpart of the transverse section taken from substantially intermediateportion of the material. The alloy material was of rectangular shapewith a size of 30 mm (length)×40 mm (width)×20 mm (thickness). The X-raydiffraction pattern of the material only had abroad halo peak,indicating the single phase constitution of the amorphous phase. Theoptical micrograph of the central part of the transverse cross sectionalso showed no contrast indicative of the precipitation of the crystalphase to confirm the results of the X-ray diffractometry. These resultsindicate that the alloy material was formed from the molten metal whichwas completely free from the molten metal of the region in contact withor in the vicinity of the copper hearth (copper crucible bed) at atemperature below the melting point which invites co-presence of theamorphous and crystal phases, and that nonuniform nucleation due to thecontact of the molten metal in the copper hearth with the coppercrucible bed is prevented by the present method.

[0107]FIG. 8 represents a DSC curve of the Zr₅₅Al₁₀Cu₃₀Ni₁₅ alloymaterial produced in Example 14 for the central amorphous part of thesection taken from substantially intermediate portion of the material.The initiation of endothermic reaction by glass transition and theinitiation of the exothermic reaction by crystallization are found at680° C. and 760° C., respectively, and the supercooled liquid state isfound over a considerably wide temperature range of 80° C. The resultsas described above demonstrate the capability of the forging process toproduce a really glassy metal, and in addition, capability of theforging process to produce a large-sized bulk alloy material solelycomprising the amorphous phase by suppressing the occurrence of thenonuniform nucleation. The Vickers hardness (Hv) of the large-sizedamorphous bulk alloy material produced in Example 14 was measured to be540, which is a value equivalent with the value (550) measured for thecorresponding sampling in the form of a ribbon.

[0108]FIG. 9 is a photomicrograph (×500) showing the metal texture ofthe Zr₅₅Al₁₀Cu₃₀Ni₁₅ alloy material produced in Example 14 for thecentral amorphous part of the transverse section taken fromsubstantially intermediate portion of the material. This photomicrographdemonstrates that the bulk amorphous alloy material of rectangular shapeproduced is an amorphous single phase alloy material substantially freefrom crystalline phase which has been produced by avoiding thenonuniform nucleation.

[0109] As demonstrated in Table 1, all of the samples of Examples 1 to14 exhibited excellent mechanical strength, and the bulk amorphous alloyof rectangular shape produced by the cast forging process of the presentinvention is a bulk amorphous alloy which is free from casting defectssuch as cold shuts and which has excellent strength properties. Theanalysis of the sample obtained in Example 14 reveals that the bulkamorphous alloys of rectangular shape produced in the Examples areamorphous single phase alloys substantially free from crystalline phasewhich have been produced by avoiding the nonuniform nucleation.

[0110] The metallic glass production process and apparatus of thepresent invention have been described in detail by referring to variousembodiments. The present invention, however, is not limited to suchembodiments, and various modifications and design changes within thescope of the present invention should occur to those skilled in the art.

1. A process for producing a bulk metallic glass of desired shapecomprising the steps of: filling a metal material in a hearth; meltingsaid metal material by using a high-energy heat source which is capableof melting said metal material; pressing a molten metal at a temperatureabove the melting point of said metal material to deform the moltenmetal at a temperature above the melting point into the desired shape byat least one of compressive stress and shear stress, while avoidingsurfaces of the molten metal cooled to a temperature below the meltingpoint of said metal material from meeting with each other during thepressing; and cooling said molten metal at a cooling rate higher thanthe critical cooling rate of the metal material simultaneously with orafter said deformation to produce the bulk metallic glass of the desiredform.
 2. The process for producing the bulk metallic glass according toclaim 1 wherein said molten metal at a temperature above the meltingpoint of said metal material is pressed while avoiding not only themeeting of the surfaces of the molten metal cooled to a temperaturebelow the melting point of said metal material with each other but alsomeeting of such molten metal surface with another surface cooled to atemperature below the melting point of said metal material.
 3. Theprocess for producing the bulk metallic glass according to claim 1 or 2wherein said pressing and deforming of said molten metal is accomplishedby selectively rolling said molten metal at a temperature above themelting point of said metal material into the plate shape or otherdesired shape with a cooled roll for rolling.
 4. The process forproducing the bulk metallic glass according to claim 3 wherein, aftermelting said metal material filled in the hearth, the molten metal at atemperature above the melting point rising over the hearth isselectively rolled with simultaneous cooling by rotating said cooledroll and moving the hearth in relation to said high energy heat sourceand said rotating cooled roll to thereby produce a metallic glass ofplate shape or other desired shape.
 5. The process for producing thebulk metallic glass according to claim 3 wherein said hearth is of anelongated shape, and the melting, rolling of the molten metal at atemperature above the melting point, and the cooling are continuouslyconducted by using a hearth of an elongated shape and moving such hearthin relation to said high energy heat source and said rotating cooledroll to thereby continuously produce a metallic glass of elongated shapeor other desired shape.
 6. The process for producing the bulk metallicglass according to any one of claims 3 to 5 wherein said cooled roll forrolling is provided at the position corresponding the hearth with amolten metal-discharging mechanism for discharging the molten metal at atemperature higher than the melting point from the hearth, said moltenmetal-discharging mechanism being fabricated from a material of lowthermal conductivity.
 7. The process for producing the bulk metallicglass according to claim 1 or 2 wherein said pressing and deforming ofsaid molten metal is accomplished by selectively transferring saidmolten metal at a temperature above the melting point of said metalmaterial into a cavity of the desired shape in the mold provided nearsaid hearth without fluidizing the molten metal, and pressing the moltenmetal with a cooled upper mold without delay to forge the molten metalinto the desired shape together with simultaneous cooling.
 8. Theprocess for producing the bulk metallic glass according to claim 7wherein, after melting said metal material filled in the hearth, saidhearth and said lower mold is moved to right underneath said upper moldand the upper mold is descended toward said lower mold without delay tothereby selectively transfer the molten metal at a temperature above themelting point into said mold where it is pressed and cooled to producethe metallic glass of desired shape by forging.
 9. The process forproducing the bulk metallic glass according to any one of claims 3 to 5wherein said upper mold is provided at the position corresponding thehearth with a molten metal-discharging mechanism for discharging themolten metal at a temperature higher than the melting point from thehearth, said molten metal-discharging mechanism being fabricated from amaterial of low thermal conductivity.
 10. An apparatus for producing ametallic glass comprising a hearth for accommodating a metal material,means for melting said metal material in said hearth, means for pressinga molten metal which has been melted by said metal material-meltingmeans at a temperature higher than the melting temperature to deform themolten metal into the desired shape by at least one of compressivestress and shear stress, while avoiding the surfaces of the molten metalcooled to a temperature below the melting point of said metal materialfrom meeting with each other during the pressing; and a means forcooling said molten metal at a cooling rate higher than the criticalcooling rate of the metal material simultaneously with or after saiddeformation by said pressing means.
 11. The apparatus for producing themetallic glass according to claim 10 wherein said molten metal ispressed while avoiding not only the meeting of the surfaces of themolten metal cooled to a temperature below the melting point of saidmetal material with each other but also meeting of such molten metalsurface with another surface cooled to a temperature below the meltingpoint of said metal material.
 12. The apparatus for producing themetallic glass according to claim 10 or 11 wherein said pressing meansdoubles as said cooling means.
 13. The apparatus for producing themetallic glass according to any one of claims 10 to 12 wherein saidpressing means has a cooled roll for rolling and a mold provided nearsaid hearth.
 14. The apparatus for producing the metallic glassaccording to claim 13 wherein the molten metal at a temperature abovethe melting point rising over the hearth is cast into said mold by saidcooled roll by rotating said cooled roll and moving said hearth and saidmold in relation to said cooled roll and said melting means toaccomplish the rolling by said cooled roll and said mold.
 15. Theapparatus for producing the metallic glass according to claim 13 or 14wherein said hearth is of elongated shape, and the rolling and thecooling by said cooled roll and said mold is continuously conducted bymoving said hearth and said mold in relation to said cooled roll andsaid melting means.
 16. The apparatus for producing the metallic glassaccording to any one of claims 13 to 15 wherein said cooled roll forrolling is provided at the position corresponding said hearth with amolten metal-discharging mechanism for discharging the molten metal at atemperature higher than the melting point from the hearth, said moltenmetal-discharging mechanism being fabricated from a material having lowthermal conductivity.
 17. The apparatus for producing the metallic glassaccording to any one of claims 10 to 12 wherein said pressing means hasa lower mold provided near said hearth into which the molten metaldischarged from said hearth is filled, and an upper mold which forgesthe molten metal filled in said lower mold together with said lowermold.
 18. The apparatus for producing the metallic glass according toclaim 17 wherein, after melting said metal material filled in thehearth, said hearth and said lower mold are moved in relation to saidmelting means and said upper mold until said upper mold is positioned ata position opposing said hearth and said lower mold, and the upper moldis descended or the lower mold is ascended without delay to therebytransfer the molten metal from said hearth into said mold where it isforged.
 19. The apparatus for producing the metallic glass according toclaim 17 or 18 wherein said upper mold is provided at the positioncorresponding said hearth with a molten metal-discharging mechanism fordischarging the molten metal at a temperature higher than the meltingpoint from the hearth, said molten metal-discharging mechanism beingfabricated from a material having low thermal conductivity.